Currently, strong interest is directed to a double patterning process involving a first set of exposure and development to form a first pattern and a second set of exposure and development to form a pattern between the first pattern features. A number of double patterning processes are proposed. One exemplary process involves a first set of exposure and development to form a photoresist pattern having lines and spaces at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying another layer of hard mask thereon, a second set of exposure and development of a photoresist film to form a line pattern in the spaces of the first exposure, and processing the hard mask by dry etching, thereby forming a line-and-space pattern at a half pitch of the first pattern. An alternative process involves a first set of exposure and development to form a photoresist pattern having spaces and lines at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying a photoresist layer thereon, a second set of exposure and development to form a second space pattern on the remaining hard mask portion, and processing the hard mask by dry etching. In either process, the hard mask is processed by two dry etchings.
When dot patterns or thin line patterns having a high aspect ratio are formed using a positive resist film, conventional alkaline development has a likelihood of pattern collapse. A study is then made on the process of forming a resist film as a thin film, forming a hard mask below the resist film, and processing the thin film resist pattern. Typical of the hard mask process is a trilayer process based on a combination of carbon film and SOG film. As the feature size is reduced, even the resist film in thin film form suffers from a more likelihood of pattern collapse.
Formation of a dot pattern by reversal of a hole pattern is under consideration. The dot pattern is produced by forming a hole pattern via development of a resist film, transferring the hole pattern to an underlying film via dry etching, coating SOG thereon, and dry etching so that the portions of SOG buried in holes define a dot pattern. This process requires two dry etching steps, once for transfer of the resist pattern to the underlying film and twice for image reversal of the SOG film buried in holes. If the SOG can be directly buried in the resist pattern, image reversal is achievable by single dry etching. Then the process becomes simple and advantageous in cost.
Recently a highlight is put on the organic solvent development again. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkali development and organic solvent development is under study.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming process is described in Patent Document 1.
The image reversal technology using silicon compounds is known in the art. For example, Patent Document 2 discloses an image reversal process involving coating SOG on a positive EB resist pattern or negative resist pattern, and etching. Patent Document 3 discloses an image reversal process involving coating an SOG film on a resist pattern and dry etching. Patent Document 4 discloses an image reversal process involving coating an SOG material on a positive resist pattern and developing in an organic solvent to dissolve the positive resist pattern.
There are proposed silicon-containing materials for the reversal process. When a silicon-containing reversal film is coated on a resist, pattern, a choice of a solvent which does not dissolve the resist film is important. As the solvent which does not dissolve the resist film, ether compounds of 8 to 12 carbon atoms and alcohol compounds of 4 to 10 carbon atoms are described in Patent Document 6. These solvents are used to formulate a protective film-forming solution in the immersion lithography. These solvents are applicable to the silicon-containing materials for the reversal process. Patent Document 5 describes solutions of polysiloxane compounds in alcohols of 4 to 10 carbon atoms or ether compounds of 4 to 10 carbon atoms.
The silicon-containing reversal film is coated on a resist pattern having a stepped surface (i.e., raised and depressed portions). The silicon-containing film on the resist pattern must be etched back until the resist film is exposed. The thinner the silicon-containing film on the resist pattern, the shorter becomes the etch-back time. Since channels in the resist pattern must be tightly filled with the silicon-containing material to their bottom without leaving voids, the silicon-containing material must have good burying and flattening properties. Undesirably, silicone resins obtained from condensation of tri- and tetrafunctional alkoxysilanes are hard and have poor burying properties.
Patent Document 7 proposes to use hydrogensilsesquioxane as the SOG material having improved burying and flattening properties. Further a silane compound, typically trialkoxysilane having pendant glycol side chain or acryloyloxyalkyl group is co-condensed for thereby lowering the softening point and improving burying properties.